Periodic trends in electron transport through extended metal atom chains: comparison of Ru-3(dpa)(4)(NCS)(2) with its first-row analogues

Density functional theory is used to reconcile the structural, magnetic and electron transport properties of a triruthenium extended metal atom chain, Ru-3(dpa)(4)(NCS)(2). The distinct bending of the Ru-Ru-Ru core in this species is traced to strong second-order mixing between levels of sigma and pi symmetry that are near degenerate in the linear geometry. The dominant electron transport channel is formed by the LUMO, an orbital of pi* symmetry that lies just above the Fermi level of the gold electrode. The bending has a substantial impact on electron transport in that it induces a spin crossover from a quintet to a singlet which in turn brings the LUMO much closer to the Fermi level. The presence of significant net pi bonding in the metal chains also broadens the pi/pi(nb)/pi* manifold, such that the channel is not strongly perturbed by the electric field, even at a bias of 1.0 V. The presence of a robust pi symmetry conduction channel marks the triruthenium systems out as quite distinct from its first-row counterparts, Cr-3(dpa)(4)(NCS)(2) and Co-3(dpa)(4)(NCS)(2), where current flows primarily through the sigma framework.